Demands on semiconductor memory devices towards larger storage capacity and faster access speeds are increasing. The semiconductor industry offers a variety of semiconductor memory types. Semiconductor memory types may be categorized in volatile and non-volatile memories. A prominent volatile memory is the DRAM (Dynamic Random Access Memory) allowing for high speed and high capacity data storage. As non-volatile memories, the semiconductor industry is engaged in ROM (Read-only-Memory) (e.g., EPROM (Erasable Programmable ROM) and EEPROM (Electrically Erasable Programmable ROM), FeRAM (Ferroelectric RAM) and MRAM (Magnetoresistive RAM)).
With regard to FeRAM, a ferroelectric layer is used to store information. In a FeRAM having a 1T-1C (1 Transistor-1 Capacitor) storage cell design, similar in construction to a DRAM memory cell, one capacitor and one access transistor form the memory cell. Opposed to a DRAM cell capacitor having a linear dielectric, a FeRAM cell capacitor includes a dielectric structure based on ferroelectric material. This ferroelectric material has a non-linear relationship between the applied electric field and the apparent stored charge resulting in a ferroelectric characteristic in the form of a hysteresis loop. Besides the 1T-1C FeRAM concept, an alternative cell concept allowing for an even more compact cell design is the 1T (1 Transistor) FeRAM based on a ferroelectric field effect transistor (FeFET). In the FeFET, the gate isolation includes a ferroelectric dielectric. The threshold voltage of the FeFET depends upon the polarization of the ferroelectric dielectric.